Stealthy flight of owls inspires engineers

By Dene Moore The Canadian Press

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Jonathan Hayward
A great grey owl dives after prey in a field on the outskirts of Ottawa on Jan. 30, 2005. Justin Jaworski, an assistant professor in Lehigh University's Department of Mechanical Engineering and Mechanics is part of a team studying the wings of owls to figure out how the birds fly so silently. They believe they may discover the key to quieter wings for aircraft and a way to reduce noise from wind turbines and other mechanical devices. THE CANADIAN PRESS/Jonathan Hayward

VANCOUVER – Inspired by a collection of Canadian owl feathers, an international team of engineers is studying the nocturnal birds of prey, hoping the mysteries of their stealthy flight might lead to improvements in the design of everything from aircraft to submarines.

The team has studied the design of owl wings in microscopic detail to try to figure out how the majestic birds remain so silent in flight, swooping down on prey without warning.

“Owls are remarkable predators. They hunt in almost complete darkness, using only their ears to weave around and capture their prey,” said Justin Jaworski, an assistant professor in Lehigh University’s Department of Mechanical Engineering and Mechanics and one of the lead researchers on the project.

“A great grey owl can go through a couple of inches of ice, can hear through that, to get its prey.

“They’re quite fantastic birds.”

It was during a visit to Cambridge University a few years ago that a retired colleague gave Jaworski and his cohorts several of his collection of owl feathers, picked up from the Owl Foundation during a visit to Ontario. He piqued their interest in finding out how the owls are engineered for such stealth, and their interest piqued others.

“Those have been our inspiration for a lot of our theoretical modelling,” he said in a recent interview.

“We’re trying to figure out by looking at the physiology of the wings, comparing them to other birds and then trying to model — both through theory and replicate experiments — trying to figure out what the physics are that are making them quieter than other birds.”

There are three wing features that are unique to owls.

They have a comb of stiff feathers along the leading edge of the wing — a group of evenly spaced fibres — a flexible fringe on the trailing edge of the wing and a soft, downy material covering the top of the wing.

Jaworski and the four other researchers from Atlantic University, Virginia Tech and Cambridge are trying to figure out how each of these features contributes to the owls’ acoustic abilities. In particular, they have looked at the serrated trailing edge of the wing — the area that creates the most noise in birds and airplanes.

The believe they can unlock the key to reducing the noise generated by any type of blade, with applications for aircraft, wind turbines and other mechanical devices.

“How we got onto this actually was the navy was interested in maybe designing quieter submarine holes, or at least being able to tailor the structure of a submarine hole to be quieter under water,” Jaworski said.

Three years into their ongoing study, they’ve discovered that the downy material on the top of an owl’s wing has a unique structure that may act to reduce noise.

“It feels like commercial velvet. I has the same kind of rough but compliant feeling that you’d have with a loose carpet,” he said.

Like velvet, it has perpendicular fibres that stick up like tree trunks from the surface, but the owl down’s tree trunks have branches that grow longer near the top, where they overlap.

“What you end up getting is this kind of jungle structure, where you have a canopy of interlocking fibres which creates this buffer layer between the wing and the outside air,” he explained.

The team will present its research at a meeting of the American Physical Society that begins Sunday in Pittsburgh, Pa.